1. Field of the Invention
The present invention relates to an image pickup apparatus and an optical apparatus arranged to pick up right and left parallactic images.
2. Description of Related Art
In recent years, a variety of stereoscopic video display apparatuses have been proposed for stereoscopically displaying video images picked up by an image pickup apparatus, such as a video camera or an electronic still camera. Heretofore, there is known a stereoscopic video display apparatus in which right and left parallactic images are displayed on a monitor and are observed by the observer with liquid-crystal shutter spectacles. In such a stereoscopic video display apparatus, the states of right and left liquid crystal elements of the liquid-crystal shutter spectacles are synchronized with a video signal, so that, when a video image for the right eye and a video image for the left eye are alternately displayed on the monitor, the observer is enabled to view a video image for the right eye always with the right eye and a video image for the left eye always with the left eye. Accordingly, a video image giving a sensation of depth is observed by the observer.
More specifically, during the period when a video image for the right eye is being displayed on the monitor, the right liquid crystal element is set to a transmissive state and the left liquid crystal element is set to a non-transmissive state, while, during the period when a video image for the left eye is being displayed on the monitor, the right liquid crystal element is set to a non-transmissive state and the left liquid crystal element is set to a transmissive state.
Further, in recent years, a display of the head-mounted type or the spectacle type, i.e., the so-called head-mounted display, has been developed. In the head-mounted display, too, video images for the right eye and for the left eye are selectively displayed for the right eye and the left eye, respectively, so that the observer is enabled to view a stereoscopic video image giving a sensation of depth.
In addition, there has been proposed an arrangement in which a liquid crystal display is combined with a lenticular sheet having minute lenses of a predetermined pitch or with a mask having a predetermined pattern of aperture parts and non-aperture parts. In such an arrangement, light beams from the liquid crystal display are made to have directivity, and the directivity is made to match with a video image pattern displayed on the liquid crystal display, so that a video image for the right eye is observed with the right eye and a video image for the left eye is observed with the left eye, thereby enabling the observer to view a video image giving a sensation of depth.
Heretofore, it is general that the above-mentioned images to be displayed are picked up by the twin-lens type stereoscopic camera having two lenses. In addition, there has been proposed a camera which does not require two lenses (a photographing apparatus for stereoscopic television disclosed in Japanese Patent Publication No. Hei 8-27499). This camera has two liquid-crystal shutters, a total-reflection mirror and a half-reflection mirror, and is arranged to pick up right and left parallactic images alternately through one lens.
Further, in the case of the twin-lens type stereoscopic camera, the so-called convergence adjustment for adjusting the parallax of right and left images during photographing is required for the lenses for time-divisionally picking up right and left video images. Heretofore, in general, the convergence adjustment is performed manually.
However, since, in the case of the above-mentioned conventional twin-lens type stereoscopic camera, a video image for the right eye and a video image for the left eye are picked up for the respective lenses, if the difference between the two lenses in performance, such as magnification, deviation of an optical axis, color, brightness, distortion, field tilt or the like, occurs due to the manufacturing error of lenses, the observer tends to feel tired in viewing a stereoscopic video image, or two images tend to be unable to fuse with each other. Accordingly, it is necessary to heighten the accuracy of parts so as to match the performance of one lens with that of the other lens, or it is necessary to make the adjustment of parts if the increased accuracy of parts is still insufficient. Further, in order to absorb the difference in performance, it is necessary to take special measures, such as an electrical correction of images.
Further, in a case where zoom lenses are used in the twin-lens type stereoscopic camera, the magnification varying actions of two, right and left, lenses are required to interlock with each other during zooming with the performance of each lens adjusted. Therefore, the twin-lens type stereoscopic camera having zoom lenses necessitates high cost and a time-consuming job for manufacturing and has low mass-productivity.
In addition, two monitors are naturally needed for observing video images picked up by the twin-lens type stereoscopic camera, so that the practicability thereof is little. Further, if such two images are to be recorded, it becomes necessary to record two video signals in the state of being synchronized with each other. Therefore, a special recording apparatus is needed.
Further, in order to avoid this arrangement, it is conceivable to convert two video signals into one video signal. However, for that purpose, there is needed a special converter for use in displaying and recording right and left parallactic images alternately.
Accordingly, the twin-lens type stereoscopic camera has a large camera body as compared with that of the ordinary single-lens camera, and the whole system thereof necessitates a special apparatus, as mentioned in the foregoing. Therefore, the twin-lens type stereoscopic camera is large in size, is expensive, and has low mobility, so that it has been difficult to widely spread the twin-lens type stereoscopic camera.
On the other hand, the camera proposed in Japanese Patent Publication No. Hei 8-274999 has such a problem that, since optical paths of right and left parallactic images are combined by the half-reflection mirror to be lead to the lens, the amount of light of an image incident on the lens after being transmitted or reflected by the half-reflection mirror becomes half. Further, in the construction of this camera, theoretically, the optical path lengths of right and left parallactic images are different from each other, so that a difference in magnification between the right and left parallactic images would occur. This causes the fatigue of the observer in observing a video image picked up by the above-mentioned camera, or makes it impossible for two images to fuse with each other for a stereoscopic viewing.